DISASTER HEALTH 2016, VOL. 3, NO. 3, 78–88 http://dx.doi.org/10.1080/21665044.2016.1228326
DISASTER HEALTH BRIEFING
Distinguishing epidemiological features of the 2013–2016 West Africa Ebola virus disease outbreak James M. Shultza, Zelde Espinelb, Maria Espinolac, and Andreas Rechkemmerd a Center for Disaster & Extreme Event Preparedness (DEEP Center), University of Miami Miller School of Medicine, Miami, FL, USA; bDepartment of Psychiatry and Behavioral Health, University of Miami Miller School of Medicine and Jackson Memorial Hospital, Miami, FL, USA; cDepartment of Psychiatry and Behavioral Neuroscience, University of Cincinnati College of Medicine, Cincinnati, OH, USA; dGraduate School of Social Work (GSSW), University of Denver, Denver, CO, USA
ABSTRACT
ARTICLE HISTORY
The 2013–2016 West Africa Ebola virus disease epidemic was notable for its scope, scale, and complexity. This briefing presents a series of distinguishing epidemiological features that set this outbreak apart. Compared to one concurrent and 23 previous outbreaks of the disease over 40 years, this was the only occurrence of Ebola virus disease involving multiple nations and qualifying as a pandemic. Across multiple measures of magnitude, the 2013–2016 outbreak was accurately described using superlatives: largest and deadliest in terms of numbers of cases and fatalities; longest in duration; and most widely dispersed geographically, with outbreak-associated cases occurring in 10 nations. In contrast, the case-fatality rate was much lower for the 2013–2016 outbreak compared to the other 24 outbreaks. A population of particular interest for ongoing monitoring and public health surveillance is comprised of more than 17,000 “survivors,” Ebola patients who successfully recovered from their illness. The daunting challenges posed by this outbreak were met by an intensive international public health response. The near-exponential rate of increase of incident Ebola cases during mid-2014 was successfully slowed, reversed, and finally halted through the application of multiple disease containment and intervention strategies.
Received 3 June 2016 Revised 12 July 2016 Accepted 21 August 2016
Introduction The 2013–2016 West Africa Ebola virus disease (EVD) outbreak is a tale of the exceptional. In the 40-year history of EVD since its recognition in 1976, there have been 25 reported outbreaks, including the 2013–2016 pandemic. By the numbers, this outbreak was unmatched, with more diagnosed cases of EVD illness, more deaths, and more survivors than all other outbreaks combined. Regarding the spatial dimension, the 2013–2016 outbreak included a dense concentration of cases in the 3 contiguous nations of Guinea, Sierra Leone, and Liberia, and additional outbreak-associated cases in 7 other countries. In contrast, no previous EVD outbreak had extended beyond the borders of a single nation. In the temporal dimension, while no prior EVD epidemic lasted more than several months, the 2013–2016 Ebola episode continued
KEYWORDS
Ebola; Ebola virus disease; epidemiology; EVD; outbreak; pandemic; PHEIC; Public Health Emergency of International Concern
for 2 y and 4 months, from index case to declaration of the cessation of viral transmission. he 2013–2016 outbreak was of such scope and scale that it qualified as a pandemic, a natural biological disaster, and a Public Health Emergency of International Concern. The human health and security threats associated with this epidemic were unequaled in the history of Ebola. This briefing provides narrative, supported by a series of detailed tables and figures, to illustrate the defining features of the 2013–2016 EVD pandemic (Table 1).
Ebola virus disease The history of EVD dates back 40 y to the initial epidemiological and clinical characterization of this disease in 1976 during 2 near-simultaneous outbreaks, caused by 2 related strains of the virus, occurring in 2 neighboring African nations.1 These
CONTACT James M. Shultz, M.S. Ph.D. [email protected] 251 174 St. #2319, Sunny Isles Beach, FL 33160, USA. Color versions of one or more of the figures in this article can be found online at www.tandfonline.com/kdsh. © 2016 Taylor & Francis
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Table 1. Distinguishing features of the 2013-2016 West Africa Ebola Virus Disease (EVD) Outbreak. Defining features Natural biological disaster Pandemic: only EVD outbreak that qualified as a pandemic Public Health Emergency of International Concern (PHEIC) August 8, 2014 – March 29, 2016 Epidemiologic indicators EVD cases: highest number of cases (28,652 cases through March 2016) EVD deaths: highest number of deaths (11,325 deaths through March 2016) EVD survivors: highest number of survivors (estimate: 17,300 survivors) Duration: longest EVD outbreak in history (December 2013 – March 2016) Geographic footprint: 28,616 cases reported in Guinea, Sierra Leone, Liberia 36 cases distributed in 7 additional nations Geographic footprint: outbreak occurred in nations with no previous EVD cases Urban spread: first EVD outbreak to spread intensively in urban centers Spread via air travel: first EVD outbreak involving case diagnosis in developed nations as a result of air travel of infected persons from Ebola endemic areas Impact on health care workers (HCWs) EVD cases: highest number of HCW cases (898 HCW cases) EVD deaths: highest number of HCW deaths (518 HCW deaths) EVD survivors: highest number of HCW survivors (estimate: 380 survivors) Higher case fatality rate for HCWs (57.7%) than for non-HCWs (38.9%)
episodes were notable for both the severity of symptoms and the high case-fatality rate. The outbreak in Zaire (present-day Democratic Republic of Congo-DRC) had 318 cases and an 88 percent case-fatality rate; higher than the 53 percent death rate among 284 cases in the South Sudan epidemic. Ebola virus disease (EVD) is a severe, communicable, viral illness in humans that is frequently fatal (Table 2).2,3 Symptoms initially include some combination of headache, muscle pain, fever, weakness and malaise and may progress to diarrhea, vomiting, abdominal pain, and unexplained hemorrhage. Ebola virus symptoms typically appear 8 to 10 d following infection (range: 2–21 days). The percentage of ill persons who die from the disease (the “case-fatality rate”) is approximately 50 percent (range: 25–90 percent). Table 2 provides a detailed epidemiological description of the Ebola virus (the “infectious agent”) and EVD illness including the important links comprising Ebola’s “chain of infection.”2,3,4
2013–2016 West Africa EVD outbreak synopsis The outbreak was first reported on March 21, 2014 by the Guinea Ministry of Health,5 after several months
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when multiple chains of viral transmission went unrecognized.1,6 During the 2013–2016 Ebola pandemic, epidemiologists were able to trace the outbreak back to its source in real time.7-9 Their investigations led to the identification of the index case, the outbreak’s “Patient Zero,” a 2-year-old child from a small village of 31 households in the Gueckedou Prefecture of Guinea.7 The trigger event for this unprecedented EVD pandemic appears to have been a single instance of a wild animal to human viral transmission of Ebola virus to this young boy whose play area was beneath a grove of trees where infected bats were roosting. The index case quickly became a cluster. During the brief course of the child’s illness, his mother, sister, and grandmother who had cared for the children became infected; all four died.7 This earliest wave of case patients grew to include members of the extended family, community contacts, traditional healers, and health care workers. The virus spread along multiple, branching chains of infection that elongated and produced new sequences of infected persons who became ill and died in high proportions.7-9 As cases proliferated and dispersed geographically over the early months of 2014, this outbreak of a “mysterious” disease developed a critical mass and activated a public health and disease control response. It took until March 2014 to characterize the infectious disease agent and confirm its identity: Zaire ebolavirus.5 EVD cases increased steadily during April, May, and June 2014. The numbers inflected upward sharply during the months of July through November. By the time the outbreak was declared to be an international public health emergency on August 8, 2014, hundreds of new cases were being reported each week. The epidemic reached its zenith in October 2014 with almost 6,000 incident cases reported that month (Figs. 1 and 2). Meanwhile, the World Health Organization (WHO), the U.S. Centers for Disease Control and Prevention (CDC), Medecins Sans Frontieres, multiple United Nations entities, and international non-governmental organizations joined forces with local public health officials on the front lines to implement a robust response.10,11 These public health measures, coupled with an unprecedented deployment of international professionals to West Africa, ultimately succeeded in
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Table 2. Epidemiological profile of Ebola Virus Disease (EVD) and the 2013–2016 West Africa Ebola Virus Disease (EVD) Outbreak. Disaster Type
Hazard Exposure
Ebola virus disease
Ebola virus disease (EVD) is a severe, communicable, viral illness in humans that is frequently fatal. Symptoms initially include some combination of headache, muscle pain, fever, weakness, and malaise and may progress to diarrhea, vomiting, abdominal pain and unexplained hemorrhage. Ebola virus symptoms typically appear 8 to 10 d following infection (range: 2–21 days). The percentage who die from the disease (case-fatality rate) is approximately 50% (range: 25–90%).
2013–2016 West Africa EVD Outbreak Description
Multi-nation Ebola virus disease (EVD) outbreak declared to be a Public Health Emergency of International Concern (PHEIC) requiring international medical and humanitarian response.
Pandemic outbreak
A pandemic is an epidemic that traverses international borders and sweeps across several nations. The geographic reach of the 2013–2016 EVD outbreak epidemic, with a dense concentration of cases in 3 countries, and additional cases across 7 other nations on multiple continents, officially qualifies this event as a pandemic. The 2013–2016 EVD outbreak was the only EVD pandemic among 25 EVD outbreaks from 1976–2016.
Natural hazard taxonomy classification
This event is described as an international viral zoonotic communicable disease epidemic (pandemic) affecting large human populations on a scale that qualified as a natural biological disaster. In addition to the spread of Ebola virus and EVD illness, this pandemic ultimately escalated into a protracted complex emergency and humanitarian crisis with mass morbidity and a high case-fatality rate.
“Chain of infection”
For communicable diseases, the primary hazard of concern is the disease agent, a necessary and essential element for disease initiation/propagation. Epidemiological investigation of infectious diseases pivots around the concept of the “chain of infection.” This chain is comprised of 6 “links:”
1) 2) 3) 4) 5) 6)
infectious disease agent (Ebola virus), reservoir (where the agent principally “resides” in the environment), portal of exit, mode of transmission, portal of entry, and susceptible host.
Infectious agent
The infectious agent that causes Ebola is an RNA virus of the family Filoviridae, genus Ebolavirus. There are 5 distinct species: Ebola virus (Zaire ebolavirus, EBOV); Sudan virus (Sudan ebolavirus, SUDV); Ta€ı Forest virus (Ta€ı Forest ebolavirus, TAFV), Bundibugyo virus (Bundibugyo ebolavirus, BDBV), and Reston virus (Reston ebolavirus, RESTV). Three of the species, EBOV, SUDV, and BDBV, have each caused EVD outbreaks with more than 100 cases. TAFV has caused illness in a single case, and RESTV does not produce symptomatic disease in humans. EBOV is the virus implicated in the 2013–2016 West Africa EVD outbreak and 16 of 25 total EVD epidemics through June 2016.
Reservoir
Ebola is a “zoonotic” disease, and the primary reservoir includes a variety of small game animals and bats. Humans are actually “incidental hosts” and unnecessary for the survival of the Ebola virus. Outbreaks begin with human contact with infectious bodily fluids, meat, or wastes from a live animal or carcass. Once the “index” human case becomes infected, most or all of the serial transmission that takes place after that is human-to-human. The human element in EVD is central to human epidemics but inconsequential to the virus itself.
Portal of exit, mode of transmission, portal of entry
Infectious diseases spread via some mechanism that allows a non-infected person to come in contact with an infected mammal or human, or their bodily fluids, that contain the infectious agent. Human EVD outbreaks usually require initial animal-to-human transmission (“spillover”) followed by serial person-to-person transmission within human populations.
1) Wild animal-to-human transmission: Ebola does not typically reside within the human species. Initial transmission of Ebola to a single person or small number of humans is thought to involve direct contact with the bodily fluids of infected game animals or their carcasses or wastes. Animal species that may carry the Ebola virus include primates such as chimpanzees, gorillas, and monkeys; and other mammals including forest antelope, porcupines, and fruit or insectivorous bats. 2) Human-to-human direct contact transmission: Ebola next spreads from the infected index case to one or more non-infected persons through some form of direct contact transmission. The skin, blood, secretions and other bodily fluids of the infected person carry the virus that may potentially escape from the body, with the mucous membranes or broken skin serving as the “portal of exit.” The mechanism for transferring Ebola virus in the environment - the “mode of transmission” - is direct contact. Exposure of a non-infected person to the infected person’s virus-contaminated skin, bodily fluids, surfaces, or materials (e.g. clothing, bedding, clothing, medical equipment) may result in infection. Infection occurs when the virus gains access to a “susceptible host” via a “portal of entry” (skin or mucous membranes). This process may happen in an instant from a caring touch or another form of direct contact. Researchers have speculated about whether the Ebola virus can be transmitted via an airborne route but there has been little support for this conjecture.20 Sexual transmission. Sexual transmission of EBOV is very rare but verified in several (continued)
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Table 2. (Continued). cases. The WHO recommends that Ebola survivors and their sexual partners receive counseling regarding safer sexual practices (abstaining from all types of sex or using condoms consistently until the semen has twice tested negative) and receive a supply of condoms.
Place Dimension
EVD symptoms
Symptoms of Ebola virus disease. A constellation of signs and symptoms characterizes EVD. Early symptoms, frequently appearing with sudden onset, include fever, severe headache, nausea, muscle pain, intense weakness and malaise, and sore throat. These early symptoms are common to multiple illnesses, including malaria, and do not definitively differentiate EVD illness. Later symptoms, which typically signal higher Ebola virus titers and increased risk for death, include diarrhea, vomiting, impaired kidney and liver function with abdominal pain, and for a proportion of cases, both internal and external bleeding. The hemorrhagic symptoms, although much publicized and a source of fear regarding Ebola, appeared in only 18% of cases during the 2013–2016 outbreak. Usually laboratory results reveal low white blood cell and platelet counts and elevated liver enzymes.
Incubation period
The incubation period, the interval from infection with Ebola virus to symptom onset, is commonly 8 to 10 d (Range: 2–21 days)
Period of infectiousness
“Infectiousness” is the capacity of an infected person to “shed” virus that may infect another person. Persons with Ebola infection or EVD illness remain infectious as long as the Ebola virus is present in their blood or bodily fluids, a time interval that persists for up to 61 d following symptom onset.
Period of immunity
A variable proportion of patients with EVD, particularly those who receive hydration and supportive clinical care, recover successfully. These Ebola “survivors” develop antibodies that prevent future new infection with the Ebola virus for at least 10 y.
African nations
Widespread and intense transmission nations: Guinea, Sierra Leone, Liberia Other: Nigeria, Mali, Senegal United States, Italy, Spain, United Kingdom
Additional nations
Time Dimension
Countries with previous EVD outbreaks
Democratic Republic of the Congo (DRC), Gabon, South Sudan, Ivory Coast, Uganda, South Africa, Republic of the Congo (ROC) Note: No overlap with 2013–2016 outbreak nations
2013–2016 outbreak transmission patterns
Movement of EVD:
Index case
December 2013
PHEIC
Public Health Emergency of International Concern: Declared August 8, 2014 Discontinued March 29, 2016
Initial declaration of “disease free”
Date when nation was removed from the list of “intense transmission” nations: Liberia: May 9, 2015 Sierra Leone: November 7, 2015 Guinea: December 28, 2015
1) 2) 3) 4) 5)
forest/savannah (in reservoir) to rural villages to urban towns and cities (no prior urban spread) and to medical facilities spread to distant nations via air travel
capping and containing the outbreak.10,11 Case counts began a downward turn in the final months of 2014. In Liberia, EVD incidence dropped in November, while in Sierra Leone, the numbers of new cases remained high through December before falling steeply in January 2015 (Fig. 1). Total numbers of new outbreak-associated cases decelerated rapidly throughout 2015. Starting from 1,800 new illnesses reported in January 2015, monthly counts dropped below 400 during June and finally reached
the zero mark in all 3 intense transmission nations in the final months of the year.
2013–2016 West Africa EVD outbreak classification The 2013–2016 EVD outbreak was so noteworthy in the annals of infectious disease epidemiology that it can be differentiated from several vantage points. This was a pandemic, a biological disaster, and a Public
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Figure 1. Epidemic curve of Ebola virus disease cases: Guinea, Sierra Leone, Liberia, and 3-nation total by month, December 2013-March 2016.
Figure 2. Epidemic curve of Ebola virus disease deaths: Guinea, Sierra Leone, Liberia, and 3-nation total by month, December 2013-March 2016.
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Table 3. Timeline of Ebola Virus Disease (EVD) cases, deaths, survivors, case-fatality rates, affected nations, and Ebola virus species for all reported outbreaks, 1976-2016, and comparison between the numbers/rates for the 2013-2016 outbreak and all previous outbreaks combined. Year
EVD-Affected Nation(s)
1976 1976 1977 1979 1994 1994 1995 1996 1996 1996 2000 2001 2001 2002 2003 2004 2007 2007 2008 2011 2012 2012 2012 2014
D.R. Congo South Sudan D.R. Congo South Sudan Gabon Cote d’Ivoire D.R. Congo Gabon Gabon South Africa Uganda Gabon Republic of Congo Republic of Congo Republic of Congo South Sudan D.R. Congo Uganda D.R. Congo Uganda Uganda D.R. Congo Uganda D.R. Congo
Totals: 24 EVD Outbreaks, 1976-2014 2013-2016 EVD Outbreak
Guinea, Sierra Leone, Liberia, Mali, Nigeria, Senegal, Italy, Spain, England, United States
Ratios: 2013-2016 EVD outbreak to total of 24 EVD outbreaks
EVD Cases
EVD Deaths
EVD Case- Fatality Ebola Virus Survivors Rate Species
318 284 1 34 52 1 315 37 60 2 425 65 57 143 35 17 264 149 32 1 11 36 6 66
280 151 1 22 31 0 250 21 45 1 224 53 43 128 29 7 187 37 15 1 4 13 3 49
38 133 0 12 21 1 65 16 15 1 201 12 14 15 6 10 77 112 17 0 7 23 3 17
88.1 53.2 100.0 64.7 59.6 0.0 79.4 56.8 75.0 50.0 52.7 81.5 75.4 89.5 82.9 41.2 70.8 24.8 46.9 100.0 36.4 36.1 50.0 74.2
2,411
1,595
816
65.9
28,652
11,325
17,327
39.5
11.88
7.10
21.23
0.60
EBOV SUDV EBOV SUDV EBOV TAFV EBOV EBOV EBOV EBOV SUDV EBOV EBOV EBOV EBOV EBOV EBOV BDBV EBOV SUDV SUDV BDBV SUDV EBOV
EBOV
Notes. EBOV-Ebola virus (Zaire ebolavirus); SUDV-Sudan virus (Sudan ebolavirus); TAFV-Ta€ı Forest virus (Ta€ı Forest ebolavirus), BDBV-Bundibugyo virus (Bundibugyo ebolavirus)
Health Emergency of International Concern (PHEIC), one of only 4 infectious disease events ever to receive this designation from the WHO. Pandemic
The geographic range of this epidemic, including a focal concentration of cases in the 3 contiguous countries of Guinea, Sierra Leone, and Liberia in West Africa, and a scattering of additional cases across 7 other nations on 3 continents, officially defined this event as a pandemic. A pandemic is an epidemic that traverses international borders and sweeps across several nations. On this point, the 2013–2016 EVD outbreak stands alone; none of the 24 prior or concurrent EVD episodes involved multiple nations and none achieved pandemic status (Table 3, Fig. 3) Biological disaster
The 2013–2016 EVD outbreak qualified as a natural biological disaster. More precisely, when applying a
natural hazards taxonomy,12 this event would be definitively classified as an international viral zoonotic communicable disease epidemic (pandemic) affecting large human populations on a scale that qualified as a natural biological disaster. In addition to the spread of Ebola virus and EVD illness, this pandemic ultimately escalated into a protracted complex emergency and humanitarian crisis with mass morbidity and a high case-fatality rate. Public health emergency of international concern
This multi-national EVD outbreak was of such severity that the Director-General of the WHO, Dr. Margaret Chan, declared the outbreak to be a “Public Health Emergency of International Concern (PHEIC)” on August 8, 2014.13 This declaration, one that activates medical and humanitarian response assets worldwide, remained in force for 20 months prior to being discontinued on March 29, 2016.14
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Figure 3. Ebola virus disease outbreaks, 1976–2016 displaying outbreak size and Ebolavirus species. Source: http://www.cdc.gov/vhf/ ebola/outbreaks/history/distribution-map.html
Descriptive epidemiology: EVD case characteristics Total population
The 2013–2016 West Africa Ebola virus disease (EVD) pandemic dwarfed all previous Ebola disease
events.4,15-17 The 2013–2016 West Africa EVD outbreak surpassed all previous outbreaks combined in numbers of EVD cases, deaths, and survivors (Table 3). The total count of 28,652 cases, through March 2016, was 67 times larger than the second-ranking outbreak that occurred in Uganda in 2000, with 425 cases
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Table 4. 2013-2016 West Africa Ebola Virus Disease (EVD) Outbreak: EVD cases, deaths, and case-fatality rates for the total population and for health-care workers by nation through March 2016. Total Population Cases
Deaths
Nations with Widespread and Intense Transmission Guinea 3,804 2,536 10 8 3,814 2,544 Liberia
Health Care Workers Case- Fatality Rate
Cases
Deaths
Case- Fatality Rate
66.7% 80.0% 66.7%
196
100
51.0%
10,666 12 10,678
4,806 4 4,810
45.1% 33.3% 45.0%
378
192
50.8%
14,122 2 14,124
3,955 1 3,956
28.0% 50.0% 28.0%
307
221
72.0%
28,616
11,310
39.5%
881
513
58.2%
Other West African Nations Mali Nigeria Senegal
8 20 1
6 8 0
75.0% 40.0% 0.0%
0 11 0
0 5 0
NA 45.5% NA
SUBTOTAL
29
14
48.3%
11
5
45.5%
Nations Outside Africa Italy Spain United Kingdom United States
1 1 1 4
0 0 0 1
0.0% 0.0% 0.0% 25.0%
1 1 1 3
0 0 0 0
0.0% 0.0% 0.0% 0.0%
SUBTOTAL
7
1
14.3%
6
0
0.0%
28,652
11,325
39.5%
898
518
57.7%
Sierra Leone
SUBTOTAL
TOTAL
(Table 3).18 Among these cases, the total mortality was 11,325 deaths, yielding a case-fatality rate was 39.5 percent, almost 4 deaths for every 10 cases. For the 3 intensive transmission nations, the case-fatality rate ranged from 28.0 percent in Sierra Leone, to 45.0 percent in Liberia, to 66.7 percent in Guinea (Table 4). The casefatality rate of 39.5 percent was much lower than the corresponding 65.9 percent rate computed as total deaths (1,595) among total cases (2,411) for the 24 other outbreaks combined (Table 3). The total number of EVD “survivors” who recovered from illness can be approximated as the difference between total cases (28,652) and deaths (11,325), yielding more than 17,300 persons. The final rows in Table 3 highlight the relative magnitude of the outbreak in a compelling fashion. The 2013–2016 EVD pandemic had 12 times more cases, 7 times more deaths, and 21 times more survivors compared to all 24 previous EVD outbreaks combined. Health-care workers
Health-care workers who developed EVD were monitored intensively (Table 4). Working on the front lines
with high levels of exposure to Ebola virus, and initially, without the benefit of adequate personal protective equipment, basic water and sanitation in health facilities, or sufficient training on Ebola or infection control, health workers became ill in record numbers. Among 898 health professionals who were diagnosed with EVD, 518 died. The 57.7 percent case-fatality rate for health-care workers was almost 50 percent higher than the 38.9 percent case-fatality rate for nonhealth-care workers (Table 4).
Descriptive epidemiology: Place and spatial characteristics In terms of “place” or geographic distribution, the 2013– 2016 West Africa EVD outbreak was differentiated from previous outbreaks in several ways. First, the outbreak took place in 10 nations that had not previously experienced Ebola virus infection or EVD illness (Table 3, Fig. 3). Examination of the line listing in Table 3 confirms that the 24 previous outbreaks occurred in 7 nations in eastern or central Africa (Fig. 3).1 Among these, 5 nations have experienced multiple outbreaks:
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Figure 4. Distribution of Ebola virus disease cases for the widespread and intensive transmission nations of Guinea, Sierra Leone, and Liberia through March 2016. Source: Centers for Disease Control and Prevention. http://www.cdc.gov/vhf/ebola/images/west-africa-dis tribution-map.jpg; Webpage: http://www.cdc.gov/vhf/ebola/outbreaks/2014-west-africa/distribution-map.html
DRC, 7; Uganda, 5; Gabon, 4; Republic of Congo, 3; and South Sudan, 3.1 South Africa had a 2-case outbreak and Cote d’Ivoire had a single case. None of these 7 nations was affected during the 2013–2016 outbreak while conversely, all 10 nations with outbreak-associated cases had never experienced an Ebola case previously. Second, the 2013–2016 outbreak was the only multinational EVD “pandemic” in history, affecting 6 nations in Africa, 3 in Europe, and the United States. The other 24 outbreaks were limited to a single nation. Fully 99.9 percent of the EVD cases were concentrated in the 3 neighboring countries of Guinea, Sierra Leone, and Liberia; designated by the World Health Organization (WHO) as the “widespread and intense transmission” nations (Fig. 4, Table 4).18 Only 36 additional cases were diagnosed across the remaining 7 nations. These included 29 cases in the African nations of Nigeria, Mali, and Senegal; one case each in Italy, Spain, and England; and four cases in the United States (Table 4).18
Third, this outbreak was distinguished by virus penetration into susceptible, impoverished, denselypopulated metropolitan centers. While previous EVD outbreaks had been rural, relatively short-lived, and sputtering, the West Africa EVD pandemic intensified into a firestorm of urban viral spread. Fourth, this was the only outbreak where outbreakassociated cases were introduced via air travel into several highly-developed nations.
Descriptive epidemiology: Temporal characteristics The 2013–2016 outbreak was the longest-duration EVD epidemic, continuing for almost 28 months, the time period from the date of diagnosis of the index case in December 2013 to the end of the PHEIC declaration. Within the 28-month span of the outbreak, the
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PHEIC was in force for 20 months, from August 8, 2014 to March 29, 2016.13,14 As displayed in Fig. 1, the majority of EVD cases were diagnosed from August 2014 to February 2015. The time course varied across the 3 widespread transmission nations. Liberia displayed both the steepest rise in cases and the most rapid decline and became the first of the 3 nations to be declared “Ebola-free” on May 9, 2015. This declaration officially removed Liberia from the list of intense transmission nations. Sierra Leone achieved this status on November 7, 2015 and Guinea on December 28, 2015. However, there were brief bursts of “flare-up” cases (24 total cases) reported in these nations prior to March 29, 2016 when the WHO officially discontinued the public health emergency.14
Public health response Containing and halting disease transmission posed extraordinary challenges to local, regional, and international response capabilities, prompting Thomas R. Frieden, Director of the US. Centers for Disease Control and Prevention (CDC), to remark retrospectively on “how close the world came to a global catastrophe.”10,17 CDC professionals described the interlocking elements that comprised the disease control intervention: 1) conducting aggressive community-based surveillance to identify and isolate persons with EVD infection; 2) implementing “contact tracing” for all contacts of EVD cases and monitoring these individuals for the full 21-day Ebola incubation period; 3) investigating current and past EVD cases with trace-backs to identify active “chains” of transmission; 4) tracking deaths and bringing trained burial teams to safely handle the cadavers of the deceased; 5) maintaining daily case reporting; 6) educating and updating health-care workers about infection control practices; and 7) training health workers on safe procedures for donning, doffing, and working in personal protective equipment, for the mutual protection of staff and patients.6,19 This multi-faceted approach, drawing upon local, regional, and international assets, was able to stop the epidemic spread of the Ebola virus. The epidemic curves, Figures 1 and 2, serve as a testament to both the extreme surge in EVD cases and deaths in mid-
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2014, and the speed with which a concerted public health response was able to reverse these upward trends into plummeting declines.
Disclosure of potential conflicts of interest No potential conflicts of interest were disclosed.
Author note This briefing on the descriptive epidemiology of the 2013–2016 EVD epidemic is a spinoff of work that is currently underway, exploring the mental health and psychosocial dimensions of the outbreak, and specifically the role of fear-related behaviors in potentiating disease spread.4,15-17 These epidemiologic patterns have guided our collaborators and are shared for the benefit of investigators for whom this information provides useful context and for a broader readership with interest in the dynamics of this outbreak.
References [1] Bell BP, Damon IK, Jernigan DB, Kenyon TA, Nichol ST, O’Connor JP, Tappero JW. Overview, control strategies, and lessons learned in the CDC response to the 2014–2016 Ebola epidemic. MMWR 2016; 65 (3):4-11; PMID:27389903; http://dx.doi.org/10.15585/ mmwr.su6503a2 [2] World Health Organization. Ebola virus disease. Fact sheet 103, updated January 2016. Available at: http:// www.who.int/mediacentre/factsheets/fs103/en/. Accessed 21 August 2016. [3] Centers for Disease Control and Prevention. Ebola (Ebola virus disease). Available at: http://www.cdc.gov/vhf/ ebola/. Accessed 21 August 2016. [4] Shultz JM, Cooper JL, Baingana F, Espinel Z, Althouse B, Espinola M, Greene MC, McCoy CB, Johnson NF, Rechkemer A. The 2013–2016 West Africa Ebola virus disease (EVD) outbreak. In: Shultz JM, Johnson NF, Rechkemmer A (eds.). Oxford Handbook of Complex Disaster Risks. New York, NY: Oxford University Press, 2016. [5] World Health Organization. Global alert and response: Ebola virus disease (EVD). Geneva, Switzerland: World Health Organization; 2014. Available at http://www.who.int/csr/don/archive/disease/ebola/en. Accessed 21 August 2016. [6] Dixon MG, Shafer IJ. Ebola viral disease outbreak West Africa, 2014. MMWR 2014; 63(25):548-551; PMID:24964881 [7] Baize S, Pannetier D, Oestereich L, Rieger T., Koiyogui L, Magassouba N’F, Soropogui B, Sow MS, Keita S, De Clerck H, et al. Emergence of Zaire Ebola virus disease in Guinea. N Engl J Med 2014; 371 (15):1418-25; PMID:24738640; http://dx.doi.org/ 10.1056/NEJMoa1404505
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[8] WHO Ebola Response Team. Ebola virus disease in West Africa – the first 9 months of the epidemic and forward projections. N Engl J Med 2014; 371:1481-95; PMID:25244186; http://dx.doi.org/10.1056/NEJMoa1411100 [9] Briand S, Bertherat E, Cox P, Formenty P, Kieny M-P, Myhre JK, Roth C, Shindo N, Dye C. The international Ebola emergency. N Engl J Med 2014; 371 (13):1180-3; PMID:25140855; http://dx.doi.org/ 10.1056/NEJMp1409858 [10] Frieden TR. Foreword (MMWR supplement entitled “CDC’s Response to the 2014–2016 Ebola Epidemic —West Africa and United States”). MMWR 2016; 65(3):1-3; http://dx.doi.org/10.15585/mmwr. su6503a1 [11] Dahl BA, Kinzer MH, Raghunathan PL, Christie A, De Cock KM, Mahoney F, Bennett SD, Hersey S, Morgan OW. CDC’s Response to the 2014–2016 Ebola epidemic Guinea, Liberia, and Sierra Leone. MMWR 2016; 65(3):1220; http://dx.doi.org/10.15585/mmwr.su6503a3 [12] Guha-Sapir D, Hoyois P, Below R. Annual Disaster Statistical Review 2014: The Numbers and Trends. Brussels: Centre for Research on the Epidemiology Disasters (CRED), 2015, pp. 7-10. [13] World Health Organization. Statement on the 1st meeting of the IHR Emergency Committee on the 2014 Ebola outbreak in West Africa. 8 August 2014. Available at: http://www.who.int/mediacentre/news/statements/2014/ ebola-20140808/en/. Accessed 21 August 2016. [14] World Health Organization. Statement on the 9th meeting of the IHR Emergency Committee regarding the Ebola outbreak in West Africa. 29 March 2016. Available at:
[15]
[16]
[17]
[18]
[19]
[20]
http://www.who.int/mediacentre/news/statements/2016/ end-of-ebola-pheic/en/. Accessed 21 August 2016. Shultz JM, Baingana F, Neria Y. The 2014 Ebola outbreak and mental health: current status and recommended response. JAMA 2015; 313(6):567-8; PMID:25532102; http://dx.doi.org/10.1001/jama.2014.17934 Shultz JM, Althouse BM, Baingana F, Cooper JL, Espinola M, Greene MC, Espinel Z, McCoy CB, Mazurik L, Rechkemmer A. Fear factor: The unseen perils of the Ebola outbreak. Bul At Sci 2016; 72(5):1-7; http://dx. doi.org/10.1080/00963402.2016.1216515 Shultz JM, Cooper JL, Baingana F, Oquendo MA, Espinel Z, Althouse BM, Marcelin LH, Towers S, Espinola M, McCoy CB, Mazurik L, Wainberg ML, Neria Y, Rechkemmer A. The role of fear-related behaviors in the 2013–2016 West Africa Ebola virus disease outbreak. Curr Psychiatry Rep 2016 (in press). World Health Organization. Ebola situation report – 30 March 2016. Available at: http://apps.who.int/ebola/cur rent-situation/ebola-situation-report-30-march-2016. Accessed 15 August 2016. McNamara LA, Schafer IJ, Nolen LD, Gorina Y, Redd JT, Lo T, Ervin E, Henao O, Dahl BA, Morgan O, Hersey S, Knust B. Ebola surveillance – Guinea, Liberia, and Sierra Leone. MMWR 2016; 65(3):35-43; http://dx.doi.org/ 10.15585/mmwr.su6503a6 Osterholm MT, Moore KA, Kelley NS, Brosseau LM, Wong G, Murphy FA, Peters CJ, LeDuc JW, Russell PK, Van Herp M, et al. Transmission of Ebola viruses: what we know and what we do not know. mBio 2015; 6(2):e00137-15; PMID:25698835; http://dx.doi.org/10.1128/mBio.00137-15
DISASTER HEALTH BRIEFING
Distinguishing epidemiological features of the 2013–2016 West Africa Ebola virus disease outbreak James M. Shultza, Zelde Espinelb, Maria Espinolac, and Andreas Rechkemmerd a Center for Disaster & Extreme Event Preparedness (DEEP Center), University of Miami Miller School of Medicine, Miami, FL, USA; bDepartment of Psychiatry and Behavioral Health, University of Miami Miller School of Medicine and Jackson Memorial Hospital, Miami, FL, USA; cDepartment of Psychiatry and Behavioral Neuroscience, University of Cincinnati College of Medicine, Cincinnati, OH, USA; dGraduate School of Social Work (GSSW), University of Denver, Denver, CO, USA
ABSTRACT
ARTICLE HISTORY
The 2013–2016 West Africa Ebola virus disease epidemic was notable for its scope, scale, and complexity. This briefing presents a series of distinguishing epidemiological features that set this outbreak apart. Compared to one concurrent and 23 previous outbreaks of the disease over 40 years, this was the only occurrence of Ebola virus disease involving multiple nations and qualifying as a pandemic. Across multiple measures of magnitude, the 2013–2016 outbreak was accurately described using superlatives: largest and deadliest in terms of numbers of cases and fatalities; longest in duration; and most widely dispersed geographically, with outbreak-associated cases occurring in 10 nations. In contrast, the case-fatality rate was much lower for the 2013–2016 outbreak compared to the other 24 outbreaks. A population of particular interest for ongoing monitoring and public health surveillance is comprised of more than 17,000 “survivors,” Ebola patients who successfully recovered from their illness. The daunting challenges posed by this outbreak were met by an intensive international public health response. The near-exponential rate of increase of incident Ebola cases during mid-2014 was successfully slowed, reversed, and finally halted through the application of multiple disease containment and intervention strategies.
Received 3 June 2016 Revised 12 July 2016 Accepted 21 August 2016
Introduction The 2013–2016 West Africa Ebola virus disease (EVD) outbreak is a tale of the exceptional. In the 40-year history of EVD since its recognition in 1976, there have been 25 reported outbreaks, including the 2013–2016 pandemic. By the numbers, this outbreak was unmatched, with more diagnosed cases of EVD illness, more deaths, and more survivors than all other outbreaks combined. Regarding the spatial dimension, the 2013–2016 outbreak included a dense concentration of cases in the 3 contiguous nations of Guinea, Sierra Leone, and Liberia, and additional outbreak-associated cases in 7 other countries. In contrast, no previous EVD outbreak had extended beyond the borders of a single nation. In the temporal dimension, while no prior EVD epidemic lasted more than several months, the 2013–2016 Ebola episode continued
KEYWORDS
Ebola; Ebola virus disease; epidemiology; EVD; outbreak; pandemic; PHEIC; Public Health Emergency of International Concern
for 2 y and 4 months, from index case to declaration of the cessation of viral transmission. he 2013–2016 outbreak was of such scope and scale that it qualified as a pandemic, a natural biological disaster, and a Public Health Emergency of International Concern. The human health and security threats associated with this epidemic were unequaled in the history of Ebola. This briefing provides narrative, supported by a series of detailed tables and figures, to illustrate the defining features of the 2013–2016 EVD pandemic (Table 1).
Ebola virus disease The history of EVD dates back 40 y to the initial epidemiological and clinical characterization of this disease in 1976 during 2 near-simultaneous outbreaks, caused by 2 related strains of the virus, occurring in 2 neighboring African nations.1 These
CONTACT James M. Shultz, M.S. Ph.D. [email protected] 251 174 St. #2319, Sunny Isles Beach, FL 33160, USA. Color versions of one or more of the figures in this article can be found online at www.tandfonline.com/kdsh. © 2016 Taylor & Francis
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Table 1. Distinguishing features of the 2013-2016 West Africa Ebola Virus Disease (EVD) Outbreak. Defining features Natural biological disaster Pandemic: only EVD outbreak that qualified as a pandemic Public Health Emergency of International Concern (PHEIC) August 8, 2014 – March 29, 2016 Epidemiologic indicators EVD cases: highest number of cases (28,652 cases through March 2016) EVD deaths: highest number of deaths (11,325 deaths through March 2016) EVD survivors: highest number of survivors (estimate: 17,300 survivors) Duration: longest EVD outbreak in history (December 2013 – March 2016) Geographic footprint: 28,616 cases reported in Guinea, Sierra Leone, Liberia 36 cases distributed in 7 additional nations Geographic footprint: outbreak occurred in nations with no previous EVD cases Urban spread: first EVD outbreak to spread intensively in urban centers Spread via air travel: first EVD outbreak involving case diagnosis in developed nations as a result of air travel of infected persons from Ebola endemic areas Impact on health care workers (HCWs) EVD cases: highest number of HCW cases (898 HCW cases) EVD deaths: highest number of HCW deaths (518 HCW deaths) EVD survivors: highest number of HCW survivors (estimate: 380 survivors) Higher case fatality rate for HCWs (57.7%) than for non-HCWs (38.9%)
episodes were notable for both the severity of symptoms and the high case-fatality rate. The outbreak in Zaire (present-day Democratic Republic of Congo-DRC) had 318 cases and an 88 percent case-fatality rate; higher than the 53 percent death rate among 284 cases in the South Sudan epidemic. Ebola virus disease (EVD) is a severe, communicable, viral illness in humans that is frequently fatal (Table 2).2,3 Symptoms initially include some combination of headache, muscle pain, fever, weakness and malaise and may progress to diarrhea, vomiting, abdominal pain, and unexplained hemorrhage. Ebola virus symptoms typically appear 8 to 10 d following infection (range: 2–21 days). The percentage of ill persons who die from the disease (the “case-fatality rate”) is approximately 50 percent (range: 25–90 percent). Table 2 provides a detailed epidemiological description of the Ebola virus (the “infectious agent”) and EVD illness including the important links comprising Ebola’s “chain of infection.”2,3,4
2013–2016 West Africa EVD outbreak synopsis The outbreak was first reported on March 21, 2014 by the Guinea Ministry of Health,5 after several months
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when multiple chains of viral transmission went unrecognized.1,6 During the 2013–2016 Ebola pandemic, epidemiologists were able to trace the outbreak back to its source in real time.7-9 Their investigations led to the identification of the index case, the outbreak’s “Patient Zero,” a 2-year-old child from a small village of 31 households in the Gueckedou Prefecture of Guinea.7 The trigger event for this unprecedented EVD pandemic appears to have been a single instance of a wild animal to human viral transmission of Ebola virus to this young boy whose play area was beneath a grove of trees where infected bats were roosting. The index case quickly became a cluster. During the brief course of the child’s illness, his mother, sister, and grandmother who had cared for the children became infected; all four died.7 This earliest wave of case patients grew to include members of the extended family, community contacts, traditional healers, and health care workers. The virus spread along multiple, branching chains of infection that elongated and produced new sequences of infected persons who became ill and died in high proportions.7-9 As cases proliferated and dispersed geographically over the early months of 2014, this outbreak of a “mysterious” disease developed a critical mass and activated a public health and disease control response. It took until March 2014 to characterize the infectious disease agent and confirm its identity: Zaire ebolavirus.5 EVD cases increased steadily during April, May, and June 2014. The numbers inflected upward sharply during the months of July through November. By the time the outbreak was declared to be an international public health emergency on August 8, 2014, hundreds of new cases were being reported each week. The epidemic reached its zenith in October 2014 with almost 6,000 incident cases reported that month (Figs. 1 and 2). Meanwhile, the World Health Organization (WHO), the U.S. Centers for Disease Control and Prevention (CDC), Medecins Sans Frontieres, multiple United Nations entities, and international non-governmental organizations joined forces with local public health officials on the front lines to implement a robust response.10,11 These public health measures, coupled with an unprecedented deployment of international professionals to West Africa, ultimately succeeded in
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Table 2. Epidemiological profile of Ebola Virus Disease (EVD) and the 2013–2016 West Africa Ebola Virus Disease (EVD) Outbreak. Disaster Type
Hazard Exposure
Ebola virus disease
Ebola virus disease (EVD) is a severe, communicable, viral illness in humans that is frequently fatal. Symptoms initially include some combination of headache, muscle pain, fever, weakness, and malaise and may progress to diarrhea, vomiting, abdominal pain and unexplained hemorrhage. Ebola virus symptoms typically appear 8 to 10 d following infection (range: 2–21 days). The percentage who die from the disease (case-fatality rate) is approximately 50% (range: 25–90%).
2013–2016 West Africa EVD Outbreak Description
Multi-nation Ebola virus disease (EVD) outbreak declared to be a Public Health Emergency of International Concern (PHEIC) requiring international medical and humanitarian response.
Pandemic outbreak
A pandemic is an epidemic that traverses international borders and sweeps across several nations. The geographic reach of the 2013–2016 EVD outbreak epidemic, with a dense concentration of cases in 3 countries, and additional cases across 7 other nations on multiple continents, officially qualifies this event as a pandemic. The 2013–2016 EVD outbreak was the only EVD pandemic among 25 EVD outbreaks from 1976–2016.
Natural hazard taxonomy classification
This event is described as an international viral zoonotic communicable disease epidemic (pandemic) affecting large human populations on a scale that qualified as a natural biological disaster. In addition to the spread of Ebola virus and EVD illness, this pandemic ultimately escalated into a protracted complex emergency and humanitarian crisis with mass morbidity and a high case-fatality rate.
“Chain of infection”
For communicable diseases, the primary hazard of concern is the disease agent, a necessary and essential element for disease initiation/propagation. Epidemiological investigation of infectious diseases pivots around the concept of the “chain of infection.” This chain is comprised of 6 “links:”
1) 2) 3) 4) 5) 6)
infectious disease agent (Ebola virus), reservoir (where the agent principally “resides” in the environment), portal of exit, mode of transmission, portal of entry, and susceptible host.
Infectious agent
The infectious agent that causes Ebola is an RNA virus of the family Filoviridae, genus Ebolavirus. There are 5 distinct species: Ebola virus (Zaire ebolavirus, EBOV); Sudan virus (Sudan ebolavirus, SUDV); Ta€ı Forest virus (Ta€ı Forest ebolavirus, TAFV), Bundibugyo virus (Bundibugyo ebolavirus, BDBV), and Reston virus (Reston ebolavirus, RESTV). Three of the species, EBOV, SUDV, and BDBV, have each caused EVD outbreaks with more than 100 cases. TAFV has caused illness in a single case, and RESTV does not produce symptomatic disease in humans. EBOV is the virus implicated in the 2013–2016 West Africa EVD outbreak and 16 of 25 total EVD epidemics through June 2016.
Reservoir
Ebola is a “zoonotic” disease, and the primary reservoir includes a variety of small game animals and bats. Humans are actually “incidental hosts” and unnecessary for the survival of the Ebola virus. Outbreaks begin with human contact with infectious bodily fluids, meat, or wastes from a live animal or carcass. Once the “index” human case becomes infected, most or all of the serial transmission that takes place after that is human-to-human. The human element in EVD is central to human epidemics but inconsequential to the virus itself.
Portal of exit, mode of transmission, portal of entry
Infectious diseases spread via some mechanism that allows a non-infected person to come in contact with an infected mammal or human, or their bodily fluids, that contain the infectious agent. Human EVD outbreaks usually require initial animal-to-human transmission (“spillover”) followed by serial person-to-person transmission within human populations.
1) Wild animal-to-human transmission: Ebola does not typically reside within the human species. Initial transmission of Ebola to a single person or small number of humans is thought to involve direct contact with the bodily fluids of infected game animals or their carcasses or wastes. Animal species that may carry the Ebola virus include primates such as chimpanzees, gorillas, and monkeys; and other mammals including forest antelope, porcupines, and fruit or insectivorous bats. 2) Human-to-human direct contact transmission: Ebola next spreads from the infected index case to one or more non-infected persons through some form of direct contact transmission. The skin, blood, secretions and other bodily fluids of the infected person carry the virus that may potentially escape from the body, with the mucous membranes or broken skin serving as the “portal of exit.” The mechanism for transferring Ebola virus in the environment - the “mode of transmission” - is direct contact. Exposure of a non-infected person to the infected person’s virus-contaminated skin, bodily fluids, surfaces, or materials (e.g. clothing, bedding, clothing, medical equipment) may result in infection. Infection occurs when the virus gains access to a “susceptible host” via a “portal of entry” (skin or mucous membranes). This process may happen in an instant from a caring touch or another form of direct contact. Researchers have speculated about whether the Ebola virus can be transmitted via an airborne route but there has been little support for this conjecture.20 Sexual transmission. Sexual transmission of EBOV is very rare but verified in several (continued)
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Table 2. (Continued). cases. The WHO recommends that Ebola survivors and their sexual partners receive counseling regarding safer sexual practices (abstaining from all types of sex or using condoms consistently until the semen has twice tested negative) and receive a supply of condoms.
Place Dimension
EVD symptoms
Symptoms of Ebola virus disease. A constellation of signs and symptoms characterizes EVD. Early symptoms, frequently appearing with sudden onset, include fever, severe headache, nausea, muscle pain, intense weakness and malaise, and sore throat. These early symptoms are common to multiple illnesses, including malaria, and do not definitively differentiate EVD illness. Later symptoms, which typically signal higher Ebola virus titers and increased risk for death, include diarrhea, vomiting, impaired kidney and liver function with abdominal pain, and for a proportion of cases, both internal and external bleeding. The hemorrhagic symptoms, although much publicized and a source of fear regarding Ebola, appeared in only 18% of cases during the 2013–2016 outbreak. Usually laboratory results reveal low white blood cell and platelet counts and elevated liver enzymes.
Incubation period
The incubation period, the interval from infection with Ebola virus to symptom onset, is commonly 8 to 10 d (Range: 2–21 days)
Period of infectiousness
“Infectiousness” is the capacity of an infected person to “shed” virus that may infect another person. Persons with Ebola infection or EVD illness remain infectious as long as the Ebola virus is present in their blood or bodily fluids, a time interval that persists for up to 61 d following symptom onset.
Period of immunity
A variable proportion of patients with EVD, particularly those who receive hydration and supportive clinical care, recover successfully. These Ebola “survivors” develop antibodies that prevent future new infection with the Ebola virus for at least 10 y.
African nations
Widespread and intense transmission nations: Guinea, Sierra Leone, Liberia Other: Nigeria, Mali, Senegal United States, Italy, Spain, United Kingdom
Additional nations
Time Dimension
Countries with previous EVD outbreaks
Democratic Republic of the Congo (DRC), Gabon, South Sudan, Ivory Coast, Uganda, South Africa, Republic of the Congo (ROC) Note: No overlap with 2013–2016 outbreak nations
2013–2016 outbreak transmission patterns
Movement of EVD:
Index case
December 2013
PHEIC
Public Health Emergency of International Concern: Declared August 8, 2014 Discontinued March 29, 2016
Initial declaration of “disease free”
Date when nation was removed from the list of “intense transmission” nations: Liberia: May 9, 2015 Sierra Leone: November 7, 2015 Guinea: December 28, 2015
1) 2) 3) 4) 5)
forest/savannah (in reservoir) to rural villages to urban towns and cities (no prior urban spread) and to medical facilities spread to distant nations via air travel
capping and containing the outbreak.10,11 Case counts began a downward turn in the final months of 2014. In Liberia, EVD incidence dropped in November, while in Sierra Leone, the numbers of new cases remained high through December before falling steeply in January 2015 (Fig. 1). Total numbers of new outbreak-associated cases decelerated rapidly throughout 2015. Starting from 1,800 new illnesses reported in January 2015, monthly counts dropped below 400 during June and finally reached
the zero mark in all 3 intense transmission nations in the final months of the year.
2013–2016 West Africa EVD outbreak classification The 2013–2016 EVD outbreak was so noteworthy in the annals of infectious disease epidemiology that it can be differentiated from several vantage points. This was a pandemic, a biological disaster, and a Public
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Figure 1. Epidemic curve of Ebola virus disease cases: Guinea, Sierra Leone, Liberia, and 3-nation total by month, December 2013-March 2016.
Figure 2. Epidemic curve of Ebola virus disease deaths: Guinea, Sierra Leone, Liberia, and 3-nation total by month, December 2013-March 2016.
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Table 3. Timeline of Ebola Virus Disease (EVD) cases, deaths, survivors, case-fatality rates, affected nations, and Ebola virus species for all reported outbreaks, 1976-2016, and comparison between the numbers/rates for the 2013-2016 outbreak and all previous outbreaks combined. Year
EVD-Affected Nation(s)
1976 1976 1977 1979 1994 1994 1995 1996 1996 1996 2000 2001 2001 2002 2003 2004 2007 2007 2008 2011 2012 2012 2012 2014
D.R. Congo South Sudan D.R. Congo South Sudan Gabon Cote d’Ivoire D.R. Congo Gabon Gabon South Africa Uganda Gabon Republic of Congo Republic of Congo Republic of Congo South Sudan D.R. Congo Uganda D.R. Congo Uganda Uganda D.R. Congo Uganda D.R. Congo
Totals: 24 EVD Outbreaks, 1976-2014 2013-2016 EVD Outbreak
Guinea, Sierra Leone, Liberia, Mali, Nigeria, Senegal, Italy, Spain, England, United States
Ratios: 2013-2016 EVD outbreak to total of 24 EVD outbreaks
EVD Cases
EVD Deaths
EVD Case- Fatality Ebola Virus Survivors Rate Species
318 284 1 34 52 1 315 37 60 2 425 65 57 143 35 17 264 149 32 1 11 36 6 66
280 151 1 22 31 0 250 21 45 1 224 53 43 128 29 7 187 37 15 1 4 13 3 49
38 133 0 12 21 1 65 16 15 1 201 12 14 15 6 10 77 112 17 0 7 23 3 17
88.1 53.2 100.0 64.7 59.6 0.0 79.4 56.8 75.0 50.0 52.7 81.5 75.4 89.5 82.9 41.2 70.8 24.8 46.9 100.0 36.4 36.1 50.0 74.2
2,411
1,595
816
65.9
28,652
11,325
17,327
39.5
11.88
7.10
21.23
0.60
EBOV SUDV EBOV SUDV EBOV TAFV EBOV EBOV EBOV EBOV SUDV EBOV EBOV EBOV EBOV EBOV EBOV BDBV EBOV SUDV SUDV BDBV SUDV EBOV
EBOV
Notes. EBOV-Ebola virus (Zaire ebolavirus); SUDV-Sudan virus (Sudan ebolavirus); TAFV-Ta€ı Forest virus (Ta€ı Forest ebolavirus), BDBV-Bundibugyo virus (Bundibugyo ebolavirus)
Health Emergency of International Concern (PHEIC), one of only 4 infectious disease events ever to receive this designation from the WHO. Pandemic
The geographic range of this epidemic, including a focal concentration of cases in the 3 contiguous countries of Guinea, Sierra Leone, and Liberia in West Africa, and a scattering of additional cases across 7 other nations on 3 continents, officially defined this event as a pandemic. A pandemic is an epidemic that traverses international borders and sweeps across several nations. On this point, the 2013–2016 EVD outbreak stands alone; none of the 24 prior or concurrent EVD episodes involved multiple nations and none achieved pandemic status (Table 3, Fig. 3) Biological disaster
The 2013–2016 EVD outbreak qualified as a natural biological disaster. More precisely, when applying a
natural hazards taxonomy,12 this event would be definitively classified as an international viral zoonotic communicable disease epidemic (pandemic) affecting large human populations on a scale that qualified as a natural biological disaster. In addition to the spread of Ebola virus and EVD illness, this pandemic ultimately escalated into a protracted complex emergency and humanitarian crisis with mass morbidity and a high case-fatality rate. Public health emergency of international concern
This multi-national EVD outbreak was of such severity that the Director-General of the WHO, Dr. Margaret Chan, declared the outbreak to be a “Public Health Emergency of International Concern (PHEIC)” on August 8, 2014.13 This declaration, one that activates medical and humanitarian response assets worldwide, remained in force for 20 months prior to being discontinued on March 29, 2016.14
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Figure 3. Ebola virus disease outbreaks, 1976–2016 displaying outbreak size and Ebolavirus species. Source: http://www.cdc.gov/vhf/ ebola/outbreaks/history/distribution-map.html
Descriptive epidemiology: EVD case characteristics Total population
The 2013–2016 West Africa Ebola virus disease (EVD) pandemic dwarfed all previous Ebola disease
events.4,15-17 The 2013–2016 West Africa EVD outbreak surpassed all previous outbreaks combined in numbers of EVD cases, deaths, and survivors (Table 3). The total count of 28,652 cases, through March 2016, was 67 times larger than the second-ranking outbreak that occurred in Uganda in 2000, with 425 cases
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Table 4. 2013-2016 West Africa Ebola Virus Disease (EVD) Outbreak: EVD cases, deaths, and case-fatality rates for the total population and for health-care workers by nation through March 2016. Total Population Cases
Deaths
Nations with Widespread and Intense Transmission Guinea 3,804 2,536 10 8 3,814 2,544 Liberia
Health Care Workers Case- Fatality Rate
Cases
Deaths
Case- Fatality Rate
66.7% 80.0% 66.7%
196
100
51.0%
10,666 12 10,678
4,806 4 4,810
45.1% 33.3% 45.0%
378
192
50.8%
14,122 2 14,124
3,955 1 3,956
28.0% 50.0% 28.0%
307
221
72.0%
28,616
11,310
39.5%
881
513
58.2%
Other West African Nations Mali Nigeria Senegal
8 20 1
6 8 0
75.0% 40.0% 0.0%
0 11 0
0 5 0
NA 45.5% NA
SUBTOTAL
29
14
48.3%
11
5
45.5%
Nations Outside Africa Italy Spain United Kingdom United States
1 1 1 4
0 0 0 1
0.0% 0.0% 0.0% 25.0%
1 1 1 3
0 0 0 0
0.0% 0.0% 0.0% 0.0%
SUBTOTAL
7
1
14.3%
6
0
0.0%
28,652
11,325
39.5%
898
518
57.7%
Sierra Leone
SUBTOTAL
TOTAL
(Table 3).18 Among these cases, the total mortality was 11,325 deaths, yielding a case-fatality rate was 39.5 percent, almost 4 deaths for every 10 cases. For the 3 intensive transmission nations, the case-fatality rate ranged from 28.0 percent in Sierra Leone, to 45.0 percent in Liberia, to 66.7 percent in Guinea (Table 4). The casefatality rate of 39.5 percent was much lower than the corresponding 65.9 percent rate computed as total deaths (1,595) among total cases (2,411) for the 24 other outbreaks combined (Table 3). The total number of EVD “survivors” who recovered from illness can be approximated as the difference between total cases (28,652) and deaths (11,325), yielding more than 17,300 persons. The final rows in Table 3 highlight the relative magnitude of the outbreak in a compelling fashion. The 2013–2016 EVD pandemic had 12 times more cases, 7 times more deaths, and 21 times more survivors compared to all 24 previous EVD outbreaks combined. Health-care workers
Health-care workers who developed EVD were monitored intensively (Table 4). Working on the front lines
with high levels of exposure to Ebola virus, and initially, without the benefit of adequate personal protective equipment, basic water and sanitation in health facilities, or sufficient training on Ebola or infection control, health workers became ill in record numbers. Among 898 health professionals who were diagnosed with EVD, 518 died. The 57.7 percent case-fatality rate for health-care workers was almost 50 percent higher than the 38.9 percent case-fatality rate for nonhealth-care workers (Table 4).
Descriptive epidemiology: Place and spatial characteristics In terms of “place” or geographic distribution, the 2013– 2016 West Africa EVD outbreak was differentiated from previous outbreaks in several ways. First, the outbreak took place in 10 nations that had not previously experienced Ebola virus infection or EVD illness (Table 3, Fig. 3). Examination of the line listing in Table 3 confirms that the 24 previous outbreaks occurred in 7 nations in eastern or central Africa (Fig. 3).1 Among these, 5 nations have experienced multiple outbreaks:
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Figure 4. Distribution of Ebola virus disease cases for the widespread and intensive transmission nations of Guinea, Sierra Leone, and Liberia through March 2016. Source: Centers for Disease Control and Prevention. http://www.cdc.gov/vhf/ebola/images/west-africa-dis tribution-map.jpg; Webpage: http://www.cdc.gov/vhf/ebola/outbreaks/2014-west-africa/distribution-map.html
DRC, 7; Uganda, 5; Gabon, 4; Republic of Congo, 3; and South Sudan, 3.1 South Africa had a 2-case outbreak and Cote d’Ivoire had a single case. None of these 7 nations was affected during the 2013–2016 outbreak while conversely, all 10 nations with outbreak-associated cases had never experienced an Ebola case previously. Second, the 2013–2016 outbreak was the only multinational EVD “pandemic” in history, affecting 6 nations in Africa, 3 in Europe, and the United States. The other 24 outbreaks were limited to a single nation. Fully 99.9 percent of the EVD cases were concentrated in the 3 neighboring countries of Guinea, Sierra Leone, and Liberia; designated by the World Health Organization (WHO) as the “widespread and intense transmission” nations (Fig. 4, Table 4).18 Only 36 additional cases were diagnosed across the remaining 7 nations. These included 29 cases in the African nations of Nigeria, Mali, and Senegal; one case each in Italy, Spain, and England; and four cases in the United States (Table 4).18
Third, this outbreak was distinguished by virus penetration into susceptible, impoverished, denselypopulated metropolitan centers. While previous EVD outbreaks had been rural, relatively short-lived, and sputtering, the West Africa EVD pandemic intensified into a firestorm of urban viral spread. Fourth, this was the only outbreak where outbreakassociated cases were introduced via air travel into several highly-developed nations.
Descriptive epidemiology: Temporal characteristics The 2013–2016 outbreak was the longest-duration EVD epidemic, continuing for almost 28 months, the time period from the date of diagnosis of the index case in December 2013 to the end of the PHEIC declaration. Within the 28-month span of the outbreak, the
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PHEIC was in force for 20 months, from August 8, 2014 to March 29, 2016.13,14 As displayed in Fig. 1, the majority of EVD cases were diagnosed from August 2014 to February 2015. The time course varied across the 3 widespread transmission nations. Liberia displayed both the steepest rise in cases and the most rapid decline and became the first of the 3 nations to be declared “Ebola-free” on May 9, 2015. This declaration officially removed Liberia from the list of intense transmission nations. Sierra Leone achieved this status on November 7, 2015 and Guinea on December 28, 2015. However, there were brief bursts of “flare-up” cases (24 total cases) reported in these nations prior to March 29, 2016 when the WHO officially discontinued the public health emergency.14
Public health response Containing and halting disease transmission posed extraordinary challenges to local, regional, and international response capabilities, prompting Thomas R. Frieden, Director of the US. Centers for Disease Control and Prevention (CDC), to remark retrospectively on “how close the world came to a global catastrophe.”10,17 CDC professionals described the interlocking elements that comprised the disease control intervention: 1) conducting aggressive community-based surveillance to identify and isolate persons with EVD infection; 2) implementing “contact tracing” for all contacts of EVD cases and monitoring these individuals for the full 21-day Ebola incubation period; 3) investigating current and past EVD cases with trace-backs to identify active “chains” of transmission; 4) tracking deaths and bringing trained burial teams to safely handle the cadavers of the deceased; 5) maintaining daily case reporting; 6) educating and updating health-care workers about infection control practices; and 7) training health workers on safe procedures for donning, doffing, and working in personal protective equipment, for the mutual protection of staff and patients.6,19 This multi-faceted approach, drawing upon local, regional, and international assets, was able to stop the epidemic spread of the Ebola virus. The epidemic curves, Figures 1 and 2, serve as a testament to both the extreme surge in EVD cases and deaths in mid-
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2014, and the speed with which a concerted public health response was able to reverse these upward trends into plummeting declines.
Disclosure of potential conflicts of interest No potential conflicts of interest were disclosed.
Author note This briefing on the descriptive epidemiology of the 2013–2016 EVD epidemic is a spinoff of work that is currently underway, exploring the mental health and psychosocial dimensions of the outbreak, and specifically the role of fear-related behaviors in potentiating disease spread.4,15-17 These epidemiologic patterns have guided our collaborators and are shared for the benefit of investigators for whom this information provides useful context and for a broader readership with interest in the dynamics of this outbreak.
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